Thermodynamics: Exploring Heat, Work, and Energy in A-Level Science
What Is Thermodynamics?
Thermodynamics is the study of heat, work, and energy, and how they interact in physical systems.
Laws of Thermodynamics
First Law of Thermodynamics
Energy is conserved:
ΔU=Q−W\Delta U = Q – WΔU=Q−W
Where:
- ΔU\Delta UΔU: Change in internal energy (JJJ).
- QQQ: Heat added to the system (JJJ).
- WWW: Work done by the system (JJJ).
Second Law of Thermodynamics
Heat flows from hot to cold, and entropy always increases in an isolated system.
Third Law of Thermodynamics
At absolute zero (0 K0 \, \text{K}0K), the entropy of a perfect crystal is zero.
Heat Engines
Carnot Engine
The most efficient theoretical heat engine.
Efficiency:
η=1−TcTh\eta = 1 – \frac{T_c}{T_h}η=1−ThTc
Where:
- TcT_cTc: Cold reservoir temperature (KKK).
- ThT_hTh: Hot reservoir temperature (KKK).
Real-Life Heat Engines
Examples include car engines and power plants, where thermal energy is converted to mechanical work.
Applications of Thermodynamics
Refrigeration
Thermodynamics principles are used to extract heat from a cold area and release it in a warm area.
Renewable Energy
Used in the design of solar thermal power plants.
Medicine
Cryotherapy relies on thermodynamic principles for therapeutic benefits.
Example Problem
A heat engine operates between Th=600 KT_h = 600 \, \text{K}Th=600K and Tc=300 KT_c = 300 \, \text{K}Tc=300K. Find its efficiency.
- Formula:
η=1−TcTh\eta = 1 – \frac{T_c}{T_h}η=1−ThTc
- Substitute Values:
η=1−300600=0.5 or 50%\eta = 1 – \frac{300}{600} = 0.5 \, \text{or} \, 50\%η=1−600300=0.5or50%
Common Mistakes in Thermodynamic Calculations
- Forgetting to use Kelvin for temperature.
- Mixing up heat added (QQQ) and work done (WWW).
- Ignoring inefficiencies in real-world systems.
Practice Questions
- A heat engine absorbs 5,000 J5,000 \, \text{J}5,000J of heat and performs 2,000 J2,000 \, \text{J}2,000J of work. Calculate the change in internal energy.
- Explain the significance of the second law of thermodynamics.
- Describe one application of thermodynamics in renewable energy.